1. Field of the Invention
This invention relates in general to a magnetic head for magnetic storage devices, and more particularly to a method and apparatus for integrating a stair notch and a gap bump at a pole tip in a write head.
2. Description of Related Art
Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces using recording heads. Read heads are then used to read data from the tracks on the disk surfaces. Read and write heads can be formed together on a single slider.
In a disk drive, a magnetic recording head is made of read and write elements. The write element is used to record and erase data bits arranged in circular tracks on the disk while the read element plays back a recorded magnetic signal. The magnetic recording head is mounted on a slider that is connected to a suspension arm, the suspension arm urging the slider toward a magnetic storage disk. When the disk is rotated the slider flies above the surface of the disk on a cushion of air which is generated by the rotating disk.
Layered thin film structures are typically used in the manufacture of read and write heads. In write heads, thin film structures provide high areal density, which is the amount of data stored per unit of disk surface area, and in read heads they provide high resolution. A thin film write head may have two pole pieces, namely, a top pole piece (colloquially referred to as “P2”) and a bottom pole piece (“P1”). A write head generally has two regions, denoted a pole tip region and a back region. The pole pieces are formed from thin magnetic material films and converge in the pole tip region at a magnetic recording gap, and in the back region at a back gap.
At least one coil layer is embedded in an insulation stack. A nonmagnetic write gap layer is located between the pole tips of the first and second pole pieces and the first and second pole pieces are magnetically connected at the back gap. Processing circuitry digitally energizes the write coil, which induces flux into the first and second pole pieces so that flux signals bridge across the write gap at the ABS to write the aforementioned signal field or magnetized bits into the track of the rotating disk.
A write head also has two pole tips, sometimes denoted “P1T” and “P2T”, which are associated with and are extensions of the poles P1 and P2, respectively. The pole tips, which are relatively defined in their shape and size in contrast to the pole pieces, are separated from each other by a thin layer of non-magnetic material such as alumina or Rhodium, referred to as a gap. As a magnetic disk is spinning beneath a write head, the P2 pole tip P2T trails the P1 pole tip P1T and is therefore the last to induce flux on the disk. Thus, the P2T dimension predominantly defines the write track width of the write head, and is generally considered an important feature.
The write track width, which is related to the width “P2B” of the bottom of the pole P2, is especially important because it limits the areal density of a magnetic disk. A write head is typically rated by its areal density, which is a product of its linear bit density and its track width density. The linear bit density is the number of bits that can be written per linear inch along the track of a rotating magnetic disk and the track width density is the number of tracks that can be written per inch along a radius of the rotating magnetic disk. The linear bit density is quantified as bits per inch (BPI) and the track width density is quantified as tracks per inch (TPI). The linear bit density depends upon the thickness of the write gap layer, pole materials, throat height, fly height and media characteristics. The track width density is directly dependent upon the width of the second pole tip at the ABS. A narrower track width translates to greater tracks per inch (TPI) written on the disk, which in turn translates to greater areal density. However, with present manufacturing methods for read-write heads, the ability to produce very narrow track widths is limited. Efforts over the years to increase the areal density have resulted in increased computer storage capacities over the past few decades.
One problem encountered as the track width continues to decrease involves large side-fringing fields during recording. The fringing field, caused by flux leakage from the second pole (P2) to the first pole (P1) beyond the width of the second pole (P2), is the portion of the magnetic field that extends toward the tracks adjacent to the tracks being written.
The throat height of a write head plays a key role in obtaining a desirable BPI. The throat height of a write head is the distance from the ABS to a recessed location within the head where the first and second pole pieces first commence to separate after the ABS. The recessed location is referred to in the art as the zero throat height (ZTH). As write gap and fly height is decreased, the short throat height length is required to render high efficiencies with sufficient write field and field gradient for linear bit definition. The tolerance control of throat height variation is critical for a short throat height writer to ensure consistent writer performance and device yield. Because less magnetic flux crosses the gap as the pole layers are further separated, a short throat height is desirable in obtaining a fringing field for writing to the media that is a significant fraction of the total flux crossing the gap. Typically the throat height is determined by the curve of the second pole layer away from the gap.
Once the second pole tip is formed, it is desirable to notch the first pole piece opposite the first and second bottom corners of the second pole tip. Notching the first pole piece minimizes side writing in tracks written on the magnetic disk. As is known, when the tracks are overwritten by side writing the track density of the magnetic disk is reduced.
The flux leakage into an adjacent track is proportional to the ratio of how easy the flux may leak into an adjacent track to how easy the flux is maintained on the desired track. The ability to maintain the flux on the desired track depends more on P1 than P2 because P1 is more prone to saturation. Therefore, there is an advantage in making the P1 width wider. However, the wider P1 is, the easier it is for flux to leak into an adjacent track. The ease with which flux leaks into an adjacent track depends on the distance of the P2 to P1 footing. The deeper the notch depth, the more difficult it is for the flux to leak into an adjacent track. However, the deeper notch also makes it hard for the flux to stay on track.
When the first pole piece is notched, it has first and second sidewalls that are aligned with first and second sidewalls of the second pole tip, so that the first pole piece and the second pole tip have the same track width at the ABS. This minimizes fringing of magnetic fields from the second pole tip laterally beyond the track width (side writing) to a wide expanse of the first pole piece.
Another method for minimizing side writing in tracks written on the magnetic disk is to form a bump that it extends into a portion of the second pole tip. Because the bump extends into the second pole tip, the throat height (TH) is defined by the bump. Thus, the throat height, which is particularly important to define writer efficiency particularly for high tracks-per-inch (TPI) narrow pole width application, may be accurately defined to allow a strong field at the pole tip while minimizing the transition width, which in turn creates side writing that can make high density recording impossible.
By forming a notch in a pole and a gap bump, the width of the bottom of the second pole (P2B) sigma may be increased, i.e., differences between widths of the bottom of the second pole wafer to wafer in the manufacturing process, for the plating of the second pole (P2). Notching is used to reduce the width of the second pole tip (P2T) due to the increase in the gap thickness, which can be four times thicker. Thus, integration of a notch at the pole tip and a gap bump is difficult because these two structures are by nature perpendicular to each other and the notch process tends to destroy the bump structure.
It can be seen that there is a need for a method and apparatus for integrating a stair notch and a gap bump at a pole tip in a write head.